JPH11323287A - Heat-sensitive adhesive and heat-sensitive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain both a heat-sensitive adhesive and a heat-sensitive adhesive sheet having improved adhesiveness to a face to be slightly bonded without dropping blocking resistance. SOLUTION: This heat-sensitive adhesive comprises an ethylene-vinyl acetate copolymer having <=10% gel fraction, an ethylene-vinyl acetate copolymer having >=40% gel fraction, a tackifier and a solid plasticizer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat-sensitive adhesive which is non-tacky at room temperature but develops tackiness by heating, and after tackiness is developed, the tackiness is maintained for a while even if a heating source is removed. The present invention relates to a heat-sensitive adhesive sheet.

[0002]

2. Description of the Related Art Water-dispersible adhesives are often used in conventional heat-sensitive adhesives so that they do not have tackiness after application and drying. For example, "Glue manual"
As described in (12th edition, published by the Society of Polymer Publishing, 1980), a water-dispersed adhesive having a basic skeleton of a thermoplastic resin, a tackifier and a solid plasticizer is used as a composition. You. Among the compositions, the thermoplastic resin is a source of adhesive strength and adhesive strength. As the thermoplastic resin, acryl, styrene-acryl, styrene-butadiene, styrene-butadiene-acryl, ethylene-vinyl acetate, ethylene-vinyl acetate-vinyl chloride, ethylene-vinyl acetate-acryl, ethylene-vinyl acetate acrylate And polymers such as vinyl acetate, vinyl acetate-acrylic, ethylene-acrylic, butadiene, urethane, styrene-isoprene, isoprene, acrylonitrile-butadiene, and isobutylene, which have been used alone or in combination. In particular, acrylic, styrene-acryl, styrene-butadiene, and ethylene-vinyl acetate polymers are often used.

[0003] In addition, a solid plasticizer is basically a solid at room temperature and therefore does not impart plasticity to the resin. By melting by heating to swell or soften the resin, it is non-adhesive and heat-sensitive at room temperature. The adhesive has a function of expressing tackiness by heating. At this time, when the tackifier is present, the tackiness is more remarkably exhibited, and the practical characteristics are improved.

[0004] Heat-sensitive adhesives include paper such as high-quality paper, coated paper, art paper, vapor-deposited paper, synthetic paper, polyethylene, and the like.
It is applied on a base material such as a polyolefin resin such as polypropylene or a polyester resin represented by polyethylene terephthalate to form a heat-sensitive adhesive sheet, and the heat-sensitive adhesive sheet is labeled on a metal, glass, or plastic surface. Used as pasted. So-called poorly-adhesive plastic containers with low surface free energy, such as polyolefin resins such as polyethylene and polypropylene for food packaging applications and polyester resins typified by polyethylene phthalate for beverage bottles, cookware, and pharmaceutical bottle applications Is often used. Labels in these areas include ordinary adhesives, pressure-sensitive adhesives,
A glue or a heat-sensitive adhesive is used. However, the conventional heat-sensitive adhesive has a problem that it is difficult to adhere to a polyolefin-based or polyester-based resin, and improvement in adhesiveness has been strongly desired. In addition, when a conventional heat-sensitive adhesive sheet was attached to a plastic molded article having a lubricant, the detailed cause was not yet known, but there was a problem that the sheet peeled off from the adherend early after application. . The lubricant is used to reduce the friction between the contact surface of the plastic and the processing machine and the friction between the polymers when molding the plastic, to improve the flowability and releasability of the plastic, and to improve the processability. It is a drug to be added. As a method of addition, it is kneaded in advance in plastic or applied to the surface. Examples of the lubricant include hydrocarbons such as liquid paraffin, fatty acids, fatty acid amides, esters, alcohols, and metal soaps. The transfer of these lubricants to the molded product surface is
It is considered that this is one of the causes of the early peeling as described above.

[0005] To solve this problem, simply:
A method of lowering the glass transition temperature of the thermoplastic resin contained in the heat-sensitive adhesive is conceivable. However, lowering the glass transition temperature causes a new problem that blocking resistance deteriorates. Therefore, it is necessary to take measures to further improve the blocking resistance. As a method, a heat-sensitive adhesive further containing a wax is disclosed in JP-B-62-21835. However, as the demand for blocking resistance is becoming more and more severe, it is no longer possible to meet such demand only by blending a wax. In order to further improve the blocking resistance, when applying a heat-sensitive adhesive on the sheet, JP-A-63-172784 discloses a method of putting the smoothness of the coated surface within a certain numerical range, It is practically difficult to control the smoothness of the coated surface within a desired range.

That is, the conventional heat-sensitive adhesive has the following disadvantages. 1) It is difficult to adhere to a poorly adhered surface such as polyolefin or polyester resin. 2) When the adherend is a plastic molded article having a lubricant, peeling from the adherend occurs early after application. 3) When the improvements in 1) and 2) are performed, the blocking resistance deteriorates. If the blocking resistance is poor, there is a risk that the heat-sensitive adhesive may adhere to the contacting surface when the heat-sensitive adhesive sheet prepared by applying the heat-sensitive adhesive is wound or stacked and stored. .

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive adhesive and a heat-sensitive adhesive sheet which have improved adhesion to hardly adhered surfaces without deteriorating blocking resistance.

[0008]

That is, the first invention is an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less, an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more, and a tackifier. And a solid plasticizer.

According to a second aspect of the present invention, the ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more both have a glass transition temperature of -25 ° C. or more. A first temperature of not more than 0 ° C.
The heat-sensitive adhesive according to the invention.

In a third aspect of the present invention, an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more is added to 100 parts by weight of an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less.
The heat-sensitive adhesive according to the first or second invention, wherein the heat-sensitive adhesive is blended in an amount of up to 100 parts by weight.

[0011] A fourth invention is a method for producing an adhesive composition comprising a total of 100 parts by weight of an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more. The heat-sensitive adhesive according to any one of the first to third inventions, comprising 10 to 200 parts by weight of a imparting agent and 50 to 500 parts by weight of a solid plasticizer.

A fifth invention is a heat-sensitive adhesive sheet obtained by coating the heat-sensitive adhesive according to any one of the first to fourth inventions on a substrate.

According to a sixth aspect of the present invention, there is provided a plastic molded article having a lubricant to which the heat-sensitive adhesive sheet according to the fifth aspect is attached.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more are used as thermoplastic resins. This makes it possible to improve the adhesion to a poorly adhered surface such as a polyolefin-based or polyester-based resin or a plastic molding containing a lubricant without impairing the blocking resistance. That is, by using an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less as a thermoplastic resin in the heat-sensitive adhesive, a polyolefin-based or polyester-based resin or a plastic molded article having a lubricant or the like is used. Of the heat-sensitive adhesive by using an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more to improve the cohesive force of the heat-sensitive adhesive, It is possible to prevent the heat-sensitive adhesive sheet from being detached from the adherend early after being attached to the molded product. In the present invention, it is important that the ethylene-vinyl acetate copolymer having a gel fraction of 10% or less has a gel fraction of 10% or less, and preferably has a gel fraction of 1 to 5%. Further, ethylene-gel having a gel fraction of 40% or more
It is important that the vinyl acetate copolymer has a gel fraction of 40% or more, and preferably has a gel fraction of 50 to 75%.

Also, ethylene-gel having a gel fraction of 10% or less
Both the vinyl acetate copolymer and the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more preferably have a glass transition temperature of −25 ° C. or more and 0 ° C. or less. If the glass transition temperature is lower than −25 ° C., the blocking resistance tends to be poor, and if the glass transition temperature is higher than 0 ° C., the initial adhesive strength tends to be insufficient.

Furthermore, in the present invention, the gel fraction is 10
% To 100 parts by weight of the ethylene-vinyl acetate copolymer, it is desirable to mix 5 to 100 parts by weight of the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more,
More preferably, it is 10 to 50 parts by weight. If the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more is less than 5 parts by weight, when it is applied to a plastic molded article or the like containing a lubricant, peeling from the adherend occurs early, and the If the amount is too large, the wettability to a poorly adhered surface such as a polyolefin-based or polyester-based resin is reduced, and the initial adhesive strength tends to be insufficient.

As the tackifier for improving the adhesive performance of the heat-sensitive adhesive, conventionally known tackifiers can be used. However, those having a low softening temperature have poor blocking resistance, so that the softening temperature is 80 ° C. or higher. Are preferred. Examples of the tackifier include terpene resins, aliphatic petroleum resins, aromatic petroleum resins, cumarone-indene resins, styrene resins, phenolic resins, terpene-phenol resins, rosin derivatives (rosin, polymerized rosin, hydrogenated Rosin and their esters with glycerin, pentaerythritol and the like, resin acid dimer, etc.), among which rosin derivatives are desirable, and rosin ester compounds are particularly preferred.
These tackifiers can be used alone or in combination of two or more. That is, terpene resin and aliphatic petroleum resin, aromatic petroleum resin and cumarone-indene resin, styrene resin and phenol resin, terpene-phenol resin and rosin derivative, terpene resin and rosin derivative, aliphatic petroleum resin and rosin Derivatives, aromatic petroleum resins and rosin derivatives, cumarone-indene resins and rosin derivatives, styrene resins and rosin derivatives, phenol resins and rosin derivatives, etc.
Alternatively, a mixture of three or more of a rosin derivative, an aliphatic petroleum resin, an aromatic petroleum resin, and the like can be used.

Examples of the solid plasticizer used in the present invention include diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate, dihydroabiethyl phthalate, dimethyl isophthalate, sucrose benzoate, and ethylene glycol dibenzoate. Trimethylolethane tribenzoate, glyceride tribenzoate, pentaerythritol tetrabenzoate, sucrose octaacetate, tricyclohexyl citrate, N-cyclohexyl-p-toluenesulfonamide, and the like.
Usually, dicyclohexyl phthalate is preferably used. The particle size of the solid plasticizer has a considerable effect on the smoothness of the surface of the heat-sensitive adhesive, and if the particle size is too large, the smoothness of the surface of the heat-sensitive adhesive becomes poor, and the thermal activation time is long. Therefore, it is preferable to adjust the maximum particle diameter to 50 μm or less.

The heat-sensitive adhesive of the present invention has a gel fraction of 10
% Of the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more and the ethylene-vinyl acetate copolymer having a gel fraction of 40% or more.
10 to 200 parts by weight of the tackifier, based on 00 parts by weight,
It is preferable to contain 50 to 500 parts by weight of a solid plasticizer,
50 to 150 parts by weight of the tackifier, 200 of the solid plasticizer
More preferably, it contains 0 to 400 parts by weight.

The heat-sensitive adhesive of the present invention may further contain a filler or the like, as long as the object of the present invention is not hindered. For example, inorganic substances such as titanium oxide, alumina, kaolin and talc, paraffin, Organic substances such as natural waxes, synthetic waxes, and natural fats and oils, and resin powders can be used. Further, if necessary, a dispersant, an antifoaming agent, a thickener and the like can be used.

The heat-sensitive adhesive of the present invention can be applied to a substrate as an aqueous emulsion, an aqueous dispersion or an organic solvent solution to form a heat-sensitive adhesive sheet. The heat-sensitive adhesive can be applied to the substrate using various coating apparatuses such as a gravure coater, an air doctor coater, a floating knife coater, a die coater, and a lip coater. Further, the heat-sensitive adhesive may be applied to the entire surface of the base material, or may be applied in a stripe shape or a lattice shape. As the base material, conventionally known high-quality paper, coated paper, art paper,
Examples include paper such as vapor-deposited paper, or synthetic paper, plastic base materials such as polyolefin resins such as polyethylene and polypropylene, and polyester resins represented by polyethylene terephthalate. In addition, it is general to provide a printing layer using various inks on the side of the base material on which the heat-sensitive adhesive is not applied, and even if the application or printing of the heat-sensitive adhesive is first. good. In the case of printing after applying the heat-sensitive adhesive first, it is preferable to use an ultraviolet-curable or electron beam-curable ink so that the heat-sensitive adhesive is not activated by heat particularly when the ink is dried.

[0022]

The present invention will be specifically described below with reference to examples. However, the scope of the present invention is not limited at all by the following Examples. In the examples, “parts” means “parts by weight” and “%” means “% by weight”. [Examples 1 to 10 and Comparative Examples 1 to 4] According to the formulation shown in Table 1, a solid plasticizer, a maleic acid resin solution and water were first put into a ball mill pot, and ground for 24 hours. The vinyl acetate copolymer and the additives were added, and mixed and stirred for 5 minutes to prepare a heat-sensitive adhesive.
The obtained heat-sensitive adhesive was applied to the back side of the double-side coated paper so that the amount of application when dried was 12 g / m ² ,
After drying for a minute, a heat-sensitive adhesive sheet was obtained. The sheet was not tacky after drying. Table 1 shows the evaluation results of the adhesive strength and the blocking resistance of the heat-sensitive adhesive sheet.

[0023]

[Table 1] * 1) Nonvolatile content * 2) Toluene insoluble content * 3) Glass transition temperature * 4) Softening temperature

The adhesion and blocking resistance of the coated product were evaluated by the following methods. Adhesion force: After the heat-sensitive adhesive sheet is heated at 150 ° C. for 30 seconds to develop tackiness, the polyethylene sheet and a high-impact polystyrene sheet (hereinafter referred to as HI)
Abbreviated as PS board. ), And the adhesive strength was measured by 180-degree peeling according to JIS Z-0237, and judged according to the following criteria.
The adhesive strength was measured by leaving it in an environment of 23 ° C. and 65% for 1 day or 10 days after the application. However, the glued part is the length
100 mm. ◎ ・ ・ ・ ・ ・ ・ 500g / 15mm or more. ○ ・ ・ ・ ・ ・ ・ 200g / 15mm or more and less than 500g / 15mm. ×: Less than 200g / 15mm.

Blocking resistance: A heat-sensitive adhesive sheet is overlapped so that the heat-sensitive adhesive-coated surface and the heat-sensitive adhesive-non-coated surface face each other, and 1000 g / cm is applied to the heat-sensitive adhesive-uncoated surface of the sheet. ^After a load of ² and storage at 40 ° C. for 1 hour, the film was peeled off and evaluated according to the following criteria. ◎: There is almost no peeling resistance.・ ・ ・: Sound is generated at the time of peeling. ×: The paper fiber is pulled by peeling or the paper is broken by blocking.

As shown in Table 1, a heat-sensitive adhesive using a thermoplastic resin in combination with an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more. The heat-sensitive adhesive sheet obtained by applying the agent has good adhesion to the hardly adhered surface without impairing the blocking resistance.

[0027]

According to the present invention, a plastic molded article having a polyolefin-based or polyester-based resin and a lubricant without impairing blocking resistance, as compared with a conventional heat-sensitive adhesive sheet coated with a heat-sensitive adhesive. As a result, a heat-sensitive adhesive sheet capable of satisfying practical characteristics with respect to an adhesive force to a difficult-to-bond surface has been obtained. From the viewpoints of resource saving and economy, the industrial significance of obtaining labels, tapes, seals of packages, and the like that do not require release paper is extremely large.

Claims (6)

[Claims] 1. An ethylene-vinyl acetate copolymer having a gel fraction of 10% or less, an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more, a tackifier, and a solid plasticizer. Heat-sensitive adhesive. 2. An ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more both have a glass transition temperature of -25 ° C.
The heat-sensitive adhesive according to claim 1, wherein the temperature is not lower than 0 ° C. 3. A gel fraction of 40% based on 100 parts by weight of an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less.
3. The heat-sensitive adhesive according to claim 1, wherein 5 to 100 parts by weight of the ethylene-vinyl acetate copolymer is blended. 4. A tackifier 10 to 10 parts by weight based on a total of 100 parts by weight of an ethylene-vinyl acetate copolymer having a gel fraction of 10% or less and an ethylene-vinyl acetate copolymer having a gel fraction of 40% or more. 200 parts by weight and 50 to 5 solid plasticizer
4. The heat-sensitive adhesive according to claim 1, comprising 00 parts by weight. 5. A heat-sensitive adhesive sheet obtained by coating the heat-sensitive adhesive according to claim 1 on a substrate. 6. A plastic molded article having a lubricant to which the heat-sensitive adhesive sheet according to claim 5 is attached.